Our study identified four serum proteins, SCD1, GLPA, LIF, and NGF-β, which suggest a distinct pro-inflammatory, pro-fibrotic, and pro-angiogenetic state in the here-examined adult ‘good’ Fontan patients with a systemic LV and good exercise capacity, and without traditional laboratory signs of HF, inflammation, protein loss, or major hepatic function impairment. Here, SCD is linked to hydrops fetalis.